1. Field of the Invention
The present invention generally relates to electronic apparatus and, in a preferred embodiment thereof, more particularly relates to the mounting of integrated circuit devices on a circuit board such as the main system board of a computer.
2. Description of Related Art
in a computer system a variety of integrated circuit devices are typically mounted on the main system circuit board or xe2x80x9cmotherboardxe2x80x9d of the computer. Integrated circuit devices include, among other types, ASIC""s (application specific integrated circuits), processors, memory controllers, and I/O controllers. Using conventional design and assembly techniques, an integrated circuit device is typically mounted directly to a side of the system board using, for example, pins on the integrated circuit device that are received in conductively lined vias disposed in the system board and connected to electrically conductive signal traces branching out from the vias. The pins thus electrically couple the circuitry within the mounted integrated circuit device to these signal traces which, in turn, are extended to other system board components such as other integrated circuit devices. Various alternate connection structures, such as ball grid array and pad systems and separate pin-and-socket connector structures have been alternatively utilized to mount integrated circuit devices on computer system boards or other types of circuit boards in other types of electronic apparatus.
In order to reduce undesirable degradation in the integrated circuit device signals being routed through the system board traces coupled to the integrated circuit device, termination components are interposed within the system board signal traces. Such termination components are commonly resistors, but may include other components such as, for example, capacitors, inductors, diodes, or various combinations of these types of termination components.
Modern high signal speed integrated circuit devices are being fabricated in increasingly smaller sizes, while at the same time being provided with increasing numbers of connector pins or other connection interface structures. For example, many modern high speed integrated circuit devices have 1000 or more connector pins or pads, thus requiring a corresponding number of system board signal traces. Because of this increased pin density within a reduced spatial footprint, coupled with the increased signal speed of the integrated circuit device, the system board signal traces must often be quite close together, with each trace requiring a termination component therein, the traces must often have equal lengths, and the trace lengths between the terminating components and their associated integrated circuit device connector pins must often be equal.
Taken together, these requirements for modern high speed/high pin count integrated circuit devices make the design of the system board quite difficult from a signal trace positioning and routing standpoint. As a practical matter, when these high speed/high pin count integrated circuit devices are to be mounted on a system board it is necessary to route a considerable number of the integrated circuit device signal traces through the interior of the system board to solve the unavoidable trace congestion problem adjacent the mounted integrated circuit device.
This necessitates a considerable thickening of the entire system board to solve a trace congestion problem which is localized at the integrated circuit board area of the system boardxe2x80x94the thickening of the rest of the system board typically creating a substantial additional system board cost with no appreciable operational benefit.
It can thus be seen that there is a need for improved apparatus for mounting an integrated circuit board device to a computer main system board, or other type of circuit board, which addresses the above-mentioned circuit board signal trace routing problems. It is to this need that the present invention is directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, electronic apparatus is provided that comprises a first circuit board, representatively a computer motherboard, having first electrical circuitry; an integrated circuit device having second electrical circuitry; and a second circuit board representatively sandwiched between the first circuit board and the integrated circuit device and having third electrical circuitry.
According to a key aspect of the invention, the third electrical circuitry has a series of termination components interposed therein and operatively couples the first and second electrical circuitry. The termination components function to reduce degradation in integrated circuit device signals and representatively include resistors, but could include other types of components such as, for example, capacitors, inductors or diodes.
Because the termination components are carried by the second circuit board instead of being interposed in the electrical circuitry of the first circuit board, the first circuit board does not have to be thickened over its entire area merely to accommodate termination devices in the vicinity of the integrated circuit device thereon, and the integrated circuit device circuit routing on the first circuit board is substantially simplified. Representatively, the second circuit board has a footprint area substantially smaller than that of the first circuit board, and the terminating components are embedded within the second circuit board. Alternatively, at least some of the termination components may be surface-mounted on the second circuit board.
Illustratively, the integrated circuit device and the interstitial second circuit board are coupled by interconnected first conductive ball and pad arrays on facing side surfaces thereof, and the first and second circuit boards are coupled by interconnected second conductive ball and pad arrays on facing side surfaces thereof. Alternatively, however, the operative coupling of these three components could be effected using other types of cooperating connection structures such as, for example, connector pins and associated conductively lined through-holes. The interstitial second circuit board illustratively has a plurality of body layers which may include power and ground planes.
This unique integrated circuit device-to-circuit board connection technique illustratively utilizing an interstitial circuit board is representatively incorporated in a CPU unit portion of computer system, with the first circuit board being the CPU unit motherboard and the CPU unit further including a microprocessor and a data storage device operative to store data retrievable by the microprocessor. However, principles of the present invention may also be used to advantage in conjunction with a wide variety of other types of circuit boards in other types of electronic apparatus.
Instead of being sandwiched between the first circuit board and the integrated circuit device, the second circuit board could be mounted on the same side of the first circuit board as the integrated circuit board but spaced apart therefrom, or mounted on the opposite side of the first circuit board.